All of the 14 fatal injuries to the head and spinal cord in American football players during 1959, and several injuries and deaths during 1960, were studied in search of a common factor. Often the unyielding plastic face guard was found to have been forced upward, throwing the neck into hyperextension. A force applied to the forward projection of the face guard has a greater mechanical advantage than does force applied to the forehead or chin. The posterior rim of the helmet, below the occiput, was thereby driven against the back of the neck and frequently caused severe injury to the cervical vertebrae and spinal cord. This danger can be reduced by certain changes, described by the authors, in helmet construction.
Schneider RC, Reifel E, Crisler HO, Oosterbaan BG. Serious and Fatal Football Injuries Involving the Head and Spinal Cord. JAMA. 1961;177(6):362-367. doi:10.1001/jama.1961.03040320006002